10-7 1 0 - 1 . PURPOSE   AND   FUNCTION   OF   ENGINE AND   GENERATOR   CONTROLS   AND   INSTRU- MENTS. (cont) b. Functional Theory of   operation. (cont) to  be  an  overspeed  condition,  the overspeed acknowledge line is enabled. If the fault is an overtemperature, the engine overtemperature line is disabled. Knowledge is passed through an overspeed gate to  become the overspeed signal to one input of a set of  eight  latches. The  ENGINE  OVERTEMP line is connected directly to one of the  other  latch  inputs. The other possible engine fault, low oil pressure,   is monitored by the microprocessor at the same time that the signals on these lines are buffered and applied to two other latch inputs on  the  switch  card. Normally,  the fault signal from the microprocessor to the latches enables any signal present on a latch input to be passed to the latch  output  unchanged. However, when a fault is sensed, fault changes logic status and latches whatever signals are on the latch inputs into the latch. Changes on the latch input lines no longer affect the latch outputs; they are now locked in the logic status they were   in   when   fault   changed   logic levels. Each latch output is applied to a lamp driver,    buffered,  and  routed to the control panel. Only that line signifying a malfunction will be in a different logic state from the others. Whichever line carries the fault status signal causes the appropriate lamp on the   control   panel   to   come   on   and indicate the source of trouble to the operator. As   the   fault   is   being indicated on the control panel, the automatic engine shutdown routine is being followed. This consists  of shutting off the fuel pump drive and closing the engine fuel valve via the ARMY TM   5-6115-612-34 MARINE   CORPS   TM   6115-34/8 AIR   FORCE TO   35C2-3-471-2 NAVY AG-320B0-MME-000 fuel pump drive and fuel valve signal lines from the EECM to the engine. (b) Generator fault detection. Generator faults consist of overload, undervoltage, overvoltage, and over- temperature. These conditions are sensed by the EECM microprocessor as it monitors the overload, undervoltage, overvoltage, and  generator  overtemp lines  from  the  generator  electronic control  module  (GECM). Each line is routed  to  the  EECM  switch  card  and placed on a latch input. Each line is also  an  input  to  a  generator  fault gating circuit. Any fault, with one exception, causes the  microprocessor software  to initiate  an automatic shutdown  procedure. The one exception is  a  simultaneous undervoltage and overload, which  is  not  treated  as  a fault because it is instead detected by the GECM and appropriate steps taken by circuits in the GECM. If any other fault  is  sensed, the  output  of  the generator fault gating is enabled to send  a  fault  signal to  the  micro- processor on the generator fault line. Reception of generator fault causes the fault signal to latch the latches, shut off the fuel supply to the engine, and reenergize the contactor relay. (8)  Manual contactor disabling. Manual contactor disabling is different from automatic contactor disabling in that  this  is  an  operator-controlled process initiated because of a mal- function. To disable the contactor and stop power from flowing to the load, the  operator places the CONTACTOR switch on the control panel momentarily in the OPEN position. The operator then releases it back to the center position. As the switch moves to the OPEN position, +24 Vdc from the switch